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rpm's n' gears

Discussion in 'The Garage' started by jones, May 22, 2004.

  1. jones

    jones 1/2 ton status

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    rpm\'s n\' gears

    i'm assuming some of you run your rigs on the freeway.what rpm range are you running with what size tires and what gear ratio.ex.)a guy told me he was cruisin at 4k at 55mph,w/4.10's and 33's w/ a 3spd auto.is that typical?
     
  2. dhdescender

    dhdescender 1/2 ton status

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    Re: rpm\'s n\' gears

    @ 60mph I'll hit around 2650RPM with a 1:1 non overdrive 3 speed automatic, maybe a little higher accounting for TC slippage, this is with 5.13 gears and 42" TSL's.

    This is with a Big Block Caddy motor that hates high RPM's
     
  3. big jimmy 91

    big jimmy 91 1/2 ton status

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  4. 87BrnRsd

    87BrnRsd 1/2 ton status

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    Re: rpm\'s n\' gears

    4K is way to high to be running continuously. I am running 37's, with 4.56 gears, and a 700r4 overdrive transmission and at 65mph, I run about 2350 rpm's. Thats a pretty good rpm range to keep the engine and gas mileage happy.
    -Harrison
     
  5. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    Re: rpm\'s n\' gears

    I have 35's, 4.10's, th700, and a built 406 SBC. I cruise at about 1,700-1,800 RPM's. /forums/images/graemlins/whistling.gif
     
  6. Muddytazz

    Muddytazz 1 ton status

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    Re: rpm\'s n\' gears

    I'm running 4.10's and 33's with a TH350(standard 3-spd auto) and I'm running no where near 4K, more like around 2600
     
  7. jones

    jones 1/2 ton status

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    Re: rpm\'s n\' gears

    so a 4.10 and 31-10.5'swill be just peachy,huh? /forums/images/graemlins/thumb.gif
     
  8. trailblazer86

    trailblazer86 1/2 ton status

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    Re: rpm\'s n\' gears

    (MPH X Diff ratio X TCase Ratio X Trans Ratio X 336)÷ Tire Diameter = RPM

    Therefore:
    (55mph X 4.10 X 1 X 1 X 336)÷ 31 = 2444rpm

    Try 80mph
    (80 X 4.10 X 336) ÷ 31 = 3555RPM

    Tire size can make a huge difference
    Try 33"
    (80 X 4.10 X 336) ÷ 33 = 3339RPM

    Try overdrive and 31's
    (50MPH X 4.10 X .70 X 336) ÷ 31 = 1555RPM
    (80MPH X 4.10 X .70 X 336) ÷ 31 = 2488RPM

    This is assuming direct drive. Torque converter slippage will add a few more revs.
     

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